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Synchronous Straight-Wire (SSW) is the trademark of the authors Charles Cole and Jon Hammond. This paper is split into two parts. Part one introduces the SSW technique, explains the reasons for its development and outlines theory. Part two illustrates the technique and compares it to others. The aim of this paper is to introduce the SSW technique, which is designed to produce simultaneous synchronized movement and thereby improve efficiency. Complex concurrent movements require planning and co-ordination. An Appliance Configuration Table (ACT) facilitates this and enables the clinician to plan the required movements to correct tooth position fully before linking these to required forces for resolution. Forty cases treated using SSW are compared with other techniques. Efficiency of tooth movement is monitored using a treatment efficiency index (TEI). When compared with other techniques, SSW demonstrates improved efficiency. The technique offers a more efficient means of undertaking fixed appliance treatments and highlights the advantages of pre-programming the entire appliance (not just the brackets) and of using a coherent mechanism to facilitate 3-dimensional movements.
Clinical Relevance: The Synchronous Straight-Wire (SSW) technique is a means of organizing simultaneous treatment events by synchronizing, rather than sequencing, tooth movement.
Article
There is a clear disparity between physiologically possible rates of tooth movement and mechanically achieved treatment times. If teeth can be moved at rates of 1mm per month, and in most malocclusions the maximum displacement/movement required for any individual tooth is less than 8 mm, then why do we routinely experience treatment times in excess of 24 months?1
Such inefficiency may result from:
The concept of increasing archwire dimension to thick, rigid ‘working’ wires prior to major tooth movement.
Treatment staging (one process following another). Begg uses Stages I, II and III whilst a Straight-Wire Appliance uses level and align, etc.
SSW improves efficiency with a radically alternative approach and abandons ‘traditional’ staging. This is made possible by the form of the mini-uni-twin bracket and 0.017″ × 0.025″ thermal archwire combination. The increased inter-bracket distance created by this bracket reduces the level of force generated by any archwire engaged by a factor of 3.5.2 This principle enables a 0.017″ × 0.025″ thermal wire to be fitted whilst still delivering physiological forces at the outset of treatment. Wires with this cross-section not only have sufficient stored energy to bypass misaligned teeth, thereby increasing inter-bracket span considerably, but also facilitate the early use of auxiliaries (inter-maxillary elastics, coil spring, etc) to control tooth movement in three dimensions. This radically alters the clinician's ability to unravel a malocclusion from the outset. The essence of the technique is to retain flexibility and fluidity in order to optimize progress until all major events have occurred and to synchronize movement rather than sequence it. There is no reason why treatment events cannot be undertaken simultaneously, reducing treatment times and numbers of visits. However, multiple concurrent movements require synchronization to avoid chaos, thus the concept of Synchronous Straight–Wire, which aims to match physiologically possible rates of movement with theoretically achievable treatment times. Treatment efficiency is measured using the treatment efficiency index (TEI).
The concept
Synchronous Straight–Wire treatment events are integrated, which requires a detailed approach to the planning and monitoring of tooth movement and force application. An Appliance Configuration Table (ACT) (Figure 1) is used to plan required movement (direction and distance) and so link this to force application (elastic, coil spring, inter-arch elastics) and thus configure the mechanism to work immediately towards resolving the malocclusion and to move all the teeth at the same time in an orderly and logical fashion. Thus the entire appliance is pre-programmed or configured (not the brackets alone) to resolve all aspects of the malocclusion from the outset, and to continue to do so throughout treatment.
Figure 1. Appliance Configuration Table (ACT).
The above technique requires a specific appliance mechanism for maximal mechanical efficiency and a different approach to the planning and monitoring of treatment progress.
Material
The appliance
In order to maximize mechanical efficiency and maintain physiological principles the appliance requires the following:
Specific brackets;
Thermodynamic archwires; and
Auxiliaries.
Bracket: The mini-uni-twin bracket (3M Unitek) (Figure 2) is used because:
It increases inter-bracket span with good rotational control: the lateral slot ‘cut-outs’ and wide tie wings produce increased inter-bracket span and good rotational control, respectively.
The narrow slot means that initial archwire engagement with 0.017″ × 0.025″ wire does not express bracket tip significantly. Hence mesial forces that would otherwise express with a full width bracket are minimized when the appliance is fitted but can later be fully expressed towards the end of treatment when 0.021″ × 0.025″ wire is fitted. It is thus possible to control anchorage demands initially by controlling the expression of bracket prescription.
Bracket architecture facilitates archwire engagement even when the slot is not parallel with the arch-wire (Figure 3).
Bracket architecture allows limited tipping and a more flexible environment for movement.
Figure 2. Mini-uni-twin bracket.Figure 3.
(a, b) The lateral incisor is fully engaged after 7 weeks despite its poor relationship with the archwire and partial engagement initially. (c) Treatment completed in 24 weeks.
Archwires: 0.017″ × 0.025″ thermally activated nickel titanium is used as a base wire because:
It is sufficiently resilient to span 10–15 mm without the need to engage all teeth thereby increasing inter-bracket span and minimizing forces. (Figure 4).
Its resilience acts as an arch template and provides a secure base from which to apply elastic traction to draw tooth to wire. (Angle used exactly the same principle.) This frees the operator from the restriction of having to use the wire alone to align teeth and facilitates concurrent movements (Figure 5).
Its resilience controls canine and molar tip and roll whilst under the influence of intra/inter-arch traction (Figure 6).
Figure 4.
(a, b) Inter-bracket spans in excess of 1 cm may be achieved using large dimension flexible wires. Note alignment of the upper right central incisor in 12 weeks.Figure 5.
(a, b, c) Lateral incisors are drawn to the wire by traction at the same time as space is closed in the molar region: (a, b) 9 weeks; (b, c) 8 weeks; total 17 weeks. Note force vectoring achieved using coil/elastic to direct force appropriately.Figure 6.
(a–d) Class III traction applied from the outset. (d) Results on completion of treatment in 29 weeks.
Auxiliaries
Elastic chain: used to move teeth along or to the wire. (Figure 5a, b).
Inter-maxillary elastics: to apply inter-arch forces from the start to counteract mesial movement of the upper canine crown.
Elastic modules: to engage bracket and wire but crucially to apply traction from wire to tooth. (Figure 7). This requires specific modules that have sufficient elasticity to achieve traction. This extends the working range of the wire and moderates forces.
Coil spring: to make space and, importantly, to direct the tension of elastic chain accurately when used to draw tooth to wire. The spring stops the chain sliding to its most dependent point (Figure 5 a, b).
Figure 7.
(a, b) A combination of wire displacement and module elasticity align the lateral incisors over a period of 9 weeks. The upper lateral incisor on the left is de-rotated and aligned mainly by the elasticity of the module.
Method
Planning appliance configuration by charting required tooth movements on the ACT:
Planned movements are separated from the required forces by a segment which reminds the operator that, once fitted, the appliance will generate mesial forces.
The ACT provides visual means of designing optimal appliance configuration by mapping tooth movements (distance (mm) and direction (3D)). The forces are then charted to resolve the required movements by direct translation. The chart divides the dentition as follows:
Key teeth
Central incisors;
Canines;
First molars.
Subsidiary teeth
Lateral incisors;
Premolars;
Second molars.
Tooth movement is planned around the key teeth:
Primary focus: Correction of the key teeth in 3D.
Secondary focus: Correction of the subsidiary teeth in 3D.
Tertiary focus: Residual space closure and fine tuning of tooth position.
This hierarchical approach is used at each visit to plan movements and concentrate on the fundamental imperatives (primary focus). Once corrected, space will automatically become available for the subsidiary teeth, to which attention is now turned. Finally, residual space closure and finishing (tertiary focus) is considered to expedite finishing. Whilst planning, and at each visit, the operator concentrates on the primary focus. Attention is then given to the secondary focus in order to accommodate the subsidiary teeth. Finally, focus is again altered to the tertiary focus. Thus the fundamental imperatives (primary focus) remain at the forefront of treatment to ensure that all major objectives are achieved rapidly, whilst less important movements are planned to synchronize with them. Thus the operator considers correction of all aspects of the malocclusion at all times, and is empowered to adjust mechanics accordingly.
The ACT is therefore used to map the required movements for both direction and distance. Once completed, all necessary tooth movements may be visualized in their entirety, which then facilitates the next process of applying the necessary forces to resolve the malocclusion as a coherent synchronized process, rather than stage-by-stage.
Charting forces
Having charted the required movements, there is a clear indication of the forces required for resolution. From previous experience, the operator will perceive the relative difficulty of achieving the planned movements and be able to chart appropriately balanced forces (eg moving upper first molars mesially is achieved with greater ease than moving upper canines distally). This knowledge is vital when planning appropriate balance of force applications for appliance configuration.
The primary focus
For movement and therefore force application, the primary focus is correction of the key teeth, but the key movement to achieve and maintain is a Class I canine relationship with the uncrowded position of the lower canine. This single achievement lies at the centre of success in most malocclusions, and the aim is to achieve it quickly. Force application therefore addresses this single issue first. The upper canine must, at all times, be kept in a Class I relationship with the lower and so must move in advance of its lower counterpart. However, fitting the appliance also produces mesial forces as a reaction to canine and molar bracket tip and this is represented on the ACT. The mesialization forces after appliance fit may need to be countered immediately to prevent deterioration of the canine relationship. They are more significant in the upper arch.
The secondary focus
The subsidiary teeth are engaged directly on to the archwire if space is available and if force levels allow. If not, they may be drawn to the wire using elastic traction. By these means, aberrant subsidiary teeth are aligned concurrently whilst achieving the primary focus. Second molars are bonded at fit or as soon after as possible. Alignment of the subsidiary teeth is synchronized to occur with movements of the key teeth as (not once) space becomes available and thus these movements occur concurrently. Such forces are drawn on the chart as appropriate.
The tertiary focus
This is the achievement of final tooth position. At all times, appropriate action may be taken to achieve this by any possible means, ie bracket repositioning, de-rotation or final archwire engagement. Residual space closure is undertaken as soon as the operator is confident that this will not compromise the primary and secondary foci, which in most cases is at the fit stage, the operator having previously planned appropriate balancing of forces to achieve the three foci concurrently.
These forces are incorporated on the chart.
The treatment efficiency index (TEI)
Treatment efficiency is calculated as follows:
A high value of the TEI indicates efficient treatment. It is somewhat sobering to consider the following. If the average orthodontic treatment requires tooth movements of little more than 4 mm, achievable in 4–5 visits, with a PAR improvement of approximately 20, the TEI would be 4. Many conventional treatments struggle to exceed a TEI of 1 and so our inefficiency is profound.
Such is the theory of Synchronous Straight-Wire technique. Part two will demonstrate the technique and compare it with others.
